How to use it
- Pick a recent hard set. The weight and the reps you completed with good form, with no more than one rep left in the tank.
- Enter both. Nudge the weight with the plus and minus buttons or type it, then tap the number of reps. The estimate updates straight away, and switching between kg and lb converts the weight with you.
- Read the chart. Most programs are written in percentages of your max. Tap any row and the barbell shows exactly which plates go on each side, so "5 x 3 at 80%" becomes a bar you can load.
The three formulas
Every one rep max calculator is a curve fitted to how strength falls away as reps go up. This page runs the three most widely used and shows all of them, because the spread between them is useful information.
Epley
Weight × (1 + reps ÷ 30). The most common formula in gyms and apps. It is generous on higher-rep sets.
Brzycki
Weight × 36 ÷ (37 − reps). Close to Epley at low reps and more conservative as the reps climb.
Lombardi
Weight × reps to the power of 0.1. A gentler curve that sits between the other two for most sets.
The headline number is the average of all three. When they agree closely, trust it. When they spread apart, usually because the set was long, treat the range as the answer rather than any single number.
Past about 10 reps the estimate gets unreliable. A set of twelve says more about your conditioning than your top-end strength, and the formulas start to disagree by a lot. For a better number, work up to a heavy set of three to five.
Training by percentage
Once you have a max, percentages let a program scale to you. A rough guide to what each zone is for:
- 90% and up. Heavy singles and doubles. Practice for maxing out, used sparingly.
- 80 to 90%. Sets of two to five. The core of most strength work.
- 70 to 80%. Sets of five to eight. Volume, positions and building muscle.
- 50 to 70%. Technique, speed work, warm-ups and barbell cycling inside a conditioning workout.
The rep-max table works the other way: from your estimated max it predicts the heaviest weight you could lift for 2 to 10 reps. If a program says "build to a heavy five", that column is where to aim.
Estimate or test?
A tested single is the only true max, but it is fatiguing, carries more risk and depends on the day. Estimating from sub-maximal sets lets you track strength every week. A sensible rhythm is to estimate often, test a real single at the end of a block, and use the number you actually lifted from then on.